This project concentrates on three aspects of the structure of bacterial ribosomes. The first is details of the structure of ribosomal RNA and other ribosome-bound RNAs including tRNA and mRNA. Covalent crosslinking monitored by electron microscopy is used to map double stranded regions, single stranded regions, and more complex folding. Tritium exchange and fluorescence measurements are used to observe the structure of the smaller RNAs on the ribosomes. Of special interest is RNA components of functional sites and topological aspects of RNA structure. The second focus is interactions between RNAs on the ribosome. Current interests include whether there are any functionally significant interactions between the rRNAs or between rRNA and tRNA. Additional studies are in progress on measurements of mRNA-ribosome interactions. The third focus is an attempt to discover the arrangement of the multiple copies of proteins L7/L12 on the 50S particle, using fluorescent derivatives of this protein.